Event Horizon Telescope Captures Image of Centaurus A’s Black Hole Jet

Astronomers from the Event Horizon Telescope (EHT) Collaboration have imaged a jet in the heart of the nearby radio galaxy Centaurus A and identified the location of the galaxy’s central supermassive black hole with respect to its resolved jet core.

Distance scales uncovered in the Centaurus A jet from the extended radio structure (outer radio lobes) covering 8 degrees in the sky along the inner radio lobes and the optical galaxy (40x zoom), the inner radio jet obtained with the TANAMI telescopes (165,000x zoom) and the new highest resolution EHT image of the jet launching region (60 million x zoom). Image credit: R. Bors / CSIRO / ATNF / Feain et al. / Morganti et al. / Junkes et al. / ESO / WFI / MPIfR / APEX / Weiß et al. / NASA / CXC / CfA / Kraft et al. / TANAMI / Müller et al. / EHT / Janssen et al.

Centaurus A is located some 13 million light-years in the constellation of Centaurus.

First discovered in 1826 by the Scottish astronomer James Dunlop, it is a massive elliptical radio galaxy — a galaxy which emits strong radio waves — and is the most prominent, as well as by far the nearest, radio galaxy in the sky.

Also known as NGC 5128, LEDA 46957 and ESO 270-9, Centaurus A is also the closest active galactic nucleus to us.

Astronomers theorize that what was originally an elliptical galaxy collided with a relatively smaller spiral shaped galaxy, giving it the peculiar shape we see now.

In the heart of Centaurus A lies a supermassive black hole with the mass of 55 million solar masses.

It bridges the gap in mass and accretion rate between the supermassive black holes in Messier 87 and our own Milky Way Galaxy.

“Supermassive black holes residing in the center of galaxies like Centaurus A are feeding off gas and dust that is attracted by their enormous gravitational pull,” said Dr. Michael Janssen, an astronomer at the Max-Planck-Institut für Radioastronomie and Radboud University, and his colleagues from the EHT Collaboration.

“This process releases massive amounts of energy and the galaxy is said to become active.”

“Most matter lying close to the edge of the black hole falls in. However, some of the surrounding particles escape moments before capture and are blown far out into space: jets — one of the most mysterious and energetic features of galaxies — are born.”

Compared with previous observations, the EHT imaged the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution.

“This allows us for the first time to see and study an extragalactic radio jet on scales smaller than the distance light travels in one day,” Dr. Janssen said.

“We see up close and personally how a monstrously gigantic jet launched by a supermassive black hole is being born.”

The new EHT image shows that Centaurus A’s jet is brighter at the edges compared to the center. This phenomenon is known from other jets, but has never been seen so pronouncedly before.

“Now we are able to rule out theoretical jet models that are unable to reproduce this edge-brightening,” said Professor Matthias Kadler, an astronomer at the University of Würzburg.

“It’s a striking feature that will help us better understand jets produced by black holes.”

The astronomers found that the source structure of Centaurus A resembles the jet in Messier 87.

Furthermore, they identified the location of Centaurus A’s supermassive black hole with respect to its resolved jet core at a wavelength of 1.3 mm and concluded that the source’s event horizon shadow should be visible at terahertz frequencies.

“These data are from the same observing campaign that delivered the famous image of the black hole in Messier 87,” said Professor Heino Falcke, an astronomer at Radboud University.

“The new results show that the EHT provides a treasure trove of data on the rich variety of black holes and there is still more to come.”

The team’s paper was published in the journal Nature Astronomy.

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M. Janssen et al. Event Horizon Telescope observations of the jet launching and collimation in Centaurus A. Nat Astron, published online July 19, 2021; doi: 10.1038/s41550-021-01417-w

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